The goal of this research is to understand the structure and function of ganglion cells the output neurons in macaque retina. Certain cells in the retina the photoreceptors are stimulated by long-, medium-, or short-wavelength light. The photoreceptors pass information to bipolar cells, which in turn relay to ganglion cells, which then output to visual centers of the brain. There are also cells within the retina horizontal and amacrine that "hook up" to these circuits and share information with other cells within the retina. Some monkey species, like humans, share color vision based on three primaries red, green and blue which feed into two color-opponent channels in the brain. Our experiments are directed at determining which combinations of cell types are responsible for coding information about blue/yellow and red/green channels. We use intracellular recording and imaging in a unique preparation of living retina, combined with a three-color light, to test sensitivity and connectivity of individual cells. In 1997 we worked on three projects. (1) Physiology of horizontal cells We continued our analysis of these two types of interneurons and discovered that the first retinal synapse between photoreceptors and horizontal cells is a site for regulation of retinal sensitivity to light. We also made the first analysis of interaction between two types of photoreceptor signals in horizontal cells. (2) Physiology of bipolar cells We made the first recordings from this diverse class of interneurons and began to study photoreceptor signal organization at this processing step. (3) Physiology of amacrine cell types We made the first recordings of photoreceptor inputs to identified amacrine types and began to study the role of these interneurons in color-selective properties of ganglion cells. These projects contribute to clarifying retinal origins and circuitry, the evolution of color vision, the cellular basis for psychophysical measures, and mechanisms of disease affecting human color vision.